ultima ratio

last method, the final argument, the last resort (as force)

Notes

The last resort. Short form for the metaphor "The Last Resort of Kings and Common Men" referring to the act of declaring war; used in the names the French sniper rifle PGM Ultima Ratio and the fictional Reason weapon system. Louis XIV of France had Ultima Ratio Regum ("last argument of kings") cast on the cannons of his armies; motto of the 1st Battalion 11th Marines.